Device with rotor, stationary part or stator, and different types of liquid pocket sliders with respective specific functions

ABSTRACT

A device includes a rotor ( 5 ), a stator ( 2 ) and different types of liquid pocket sliders ( 3; 4; 10 ), each type with different and specific functions, the liquid pocket sliders preferably being mounted at the outermost surface of the rotor. The device can include ordinary pocket sliders ( 3 ), with the function of load support and bearing self-centering on the rotor ( 5 ); “sentinel” pocket sliders ( 4 ) having the function of predicting failures and/or monitoring the distribution of the load around the rotor; preload pocket sliders ( 10 ), with the function of compensating for possible unbalance of the rotor at a given velocity.

FIELD OF THE ART

The present invention generally regards the technical field relative tothe devices comprising a rotor, a stationary part arranged around therotor, and bearings that serve for supporting and allowing the rotationof the rotor with respect to the stationary part.

Specifically, the present invention relates to a device of this type, inwhich the particular arrangement of the bearings, and their nature andconformation, allow solving a series of problems that cannot be remediedwith the common ball bearings or with rollers or other bearings of thestate of the art such as foil bearings. The solved problems will all bediscussed in the following description.

In general, by “stationary part” or “stator”, it is intended a part thatis fixed with respect to a machine (e.g. a turbomachine)—said statordirectly surrounding the peripheral part of the rotor—while the term“rotor” indicates a rotating part integral with the rotating shaft, andwhose peripheral surface directly faces the stationary part. Therotating shaft constitutes the innermost rotating part of the device; ofcourse, it is coaxial with the periphery/circumference of the rotor.

For example, if the device of the invention constitutes a device mountedin a turbomachine (turbine, compressor, pump, fan, etc.), the stationarypart corresponds with the casing, while the rotor of the device isformed by the actual turbine and by all the rotating members integraltherewith; for example, in the case of a CMG (Control Moment Gyro)satellite device for controlling the attitude of a satellite, the rotorcomprises the flywheel while the stationary part comprises the stator ofthe motor (usually electric) and the box for containing the flywheel.

PRIOR ART AND PROBLEMS THEREOF

For any one rotating machine essentially constituted by a rotor, astator and bearings, it is important to prevent excessive vibrations andoscillations of the axis of the rotor system. This requirement can beparticularly important in the case of turbomachines (turbines,compressors, pumps, fans, etc.), in which the interspace or clearancebetween the stator and the rotor is usually very small, in order toreduce to a minimum the return of the flow and thus optimize thecompression ratio. A functioning that lacks vibrations is very muchdesired in any case in order to reduce the noise, improve the efficiencyof the machine and lengthen the operative life thereof. More generally,the higher the rotation velocity and the moment of inertia of the rotor,the more important it is to have a good balancing of the rotor and agood rotor-stator alignment. In fact, it is understood that the effectof an unbalance, even if small, of the rotating set could be amplifiedin an intolerable manner at high velocities, generating dangerousvibrations with the increase of amplitude, accelerating the wear both onthe bearings and on the shaft, and possibly leading to resonances forspecific critical velocities which in the end could cause the collapseof the entire system. One example of a device in which this problem isparticularly relevant is constituted by the mechanical gyroscopes, inwhich relatively large flywheels rotate at considerably velocities. Withregard to this device category, an extreme situation is that relative tothe inertial wheels, to the stabilizer wheels, and to the CMG (ControlMoment Gyros) devices, used for controlling the attitude of a satellite.In these case, in fact, the rotating element (the flywheel) must work inan environment with very low pressure, sometimes for many years ofcontinuous functioning, without the direct intervention of man, and athigh velocities (typically between 3000 and 10000 rpm). Consequently,the bearings and the relative lubrication system constitute crucialelements in these spatial apparatuses. The lubrication system of the CMGspatial devices, for example, must be able to feed the correct quantity(usually very little) of lubricant in order to reliably ensure a verylong functioning lifetime, to compensate for the degradation and wear ofthe lubricant, and to prevent the wear both of the bearings and of theshaft, or even the final seizure. In addition, since the bearingsbelonging to the prior art, used in the spatial devices for controllingthe attitude, are usually roller bearings or ball bearings, theirrotating elements must be mechanically processed with extreme precisionand hardened by special anti-wear coatings. They must not introduce anyvibration that could be harmful or extremely dangerous for the correctfunctioning of the satellite. In addition, such bearings must be capableof resisting the mechanical stresses that occur during launch, withoutsustaining any damage.

In order to solve at least some of these problems, the apparatuses ofthe prior art, not only the spatial ones, often provide for the use ofvery hard and precise bearings, a structure characterized by ratherheavy shafts as well as fairly complex lubrication systems. Indeed, theshafts and the bearings of the conventional apparatuses have thefunction of exchanging the torque with the rotor as well as the functionof maintaining the amplitude of the vibrations of the rotor at thelowest possible level. In practice, this involves the use of very heavymachines, with a high inertia of the shaft, with a rather poor ratiobetween the power developed and the mass, and consequently with a highconsumption of fuel and lubricant, without mentioning the highmanufacturing costs. In addition, if on one hand the shafts are designedand manufactured as heavy, bulky parts, on the other hand the ballbearings are higher performing if arranged around small shafts; thissignifies that the smaller the radius of the shaft, the greater itsmaximum functioning angular velocity (in rpm). Indeed, the greater thelinear velocity of the bearing, the greater the heat generated locallywith consequent loss of viscosity of the lubricant and loss of its loadcapacity. Hence, with the ball bearings, high angular velocities of theshaft are only possible using small radii, in order to maintain theliner velocity at a suitable value. Therefore, the requirements of thebearings may be antithetical to the requirements of the machine'soverall performances, and most of the time acceptable compromises mustbe reached.

Finally, the automatic functioning (without direct human intervention)of the CMG device for controlling the attitude of the satellite impliesthat automatic means must be attained for detecting the start ofperformance deterioration, possibly due to the wear of the bearingssystem. These means are often rather complex and are capable ofdetecting the start of the performance deterioration when the system hasalready been damaged to a certain extent. Indeed, they detect theconsequences in a mechanism that has already been damaged, such as thevibrations (noise) or increased friction (by means of an increased powerrequired to maintain the rotation velocity at a constant value). Inthose cases in which the vibrations are monitored for detecting theincipient degradation of the performances, piezoelectric accelerometersare often used as detectors. Such sensors/detectors are often fixed onthe bearings or on the stator, but the problem then becomes that ofbeing able to distinguish between the frequencies to be associated withdifferent conditions. Sometimes these means are not implemented and thefailure of the CMG device occurs suddenly, with dramatic consequences onthe functioning of the satellite; other times, even if these automaticmeans are employed for detecting the incipient malfunctioning, it couldbe too late to enact suitable countermeasures.

Hence, object of the present invention is to provide a new type ofstructure of a generic rotating machine, and particularly of a devicewith flywheel for controlling the attitude of a satellite, which allowssolving the above-illustrated problems of the prior art.

DESCRIPTION OF THE INVENTION

In the device according to the present invention, a particular type ofbearing is used in an original manner, non-obvious even for a manskilled in the art; such bearing, already known in the general shapethereof, is formed by pocket sliders called liquid pocket bumpersdescribed in the patent application WO 2004/053346 A1 by the sameauthor. The prior art also comprises other examples of bearings orpocket sliders based on a similar functioning principle, but it no caseknown to the author have devices similar to LPS sliders been used in themodes and for the functions described in the present invention. Forexample, the patent U.S. Pat. No. 4,170,389, by A. Eshel, regards (seeFIG. 17) a thrust bearing constituted by pockets filled with a fluid orparticles of various morphology, built for tolerating, without damage,the passage of an impurity that has inserted itself between the shaftand the block of the bearing. Or, (see FIG. 4) the liquid pocket bearing87 or 89 has a toroidal shape and acts once again as an axial thrustbearing for a discoid plate 83 integral with the shaft 82. Suchstructures are also intended for tolerating small misalignments of theshaft, nevertheless they are not adapted to carrying out the function ofstabilizing the shaft, nor for carrying out any diagnostic function orfailure prevention function. Even the bearings described in WO2004/053346 and used in the present invention, like those described inU.S. Pat. No. 5,114,244, by J. L. Dunham et Al., only serve as thrustbearings, as direct support of the rotation shaft or as support elementsfor the sliding of a piston in a cylinder, while nothing is saidregarding a preferred mounting position, which in the present inventionis indicated as the outermost possible position, around the rotor,compatibly with other design constrains. In addition, neither WO2004/053346, nor U.S. Pat. No. 5,114,244 specify the manner of designingthese sliders with self-adaptive surface for maximizing theself-centering effects thereof on the rotor. Even the elimination of thevibrations and the stability of the system are obtained, in the presentinvention, in a non-random manner, only at specific conditionscalculatable from the design in the manner which will be clarifiedbelow. In particular, the elimination of the vibrations due to animperfect balancing of the rotor is obtained, in the present invention,through the introduction of a preload in phase with the centrifugalforce deriving from the unbalance, due to elements specially set forcarrying out this function. Finally, neither WO 2004/053346, nor U.S.Pat. No. 5,114,244 provide for the use of pocket sliders whose mainfunction is not that of supporting a load but that of detecting anincipient failure in advance, i.e. that of functioning as sentinelelements in the manner described hereinbelow. The prior art alsocomprises other hydrodynamic bearings with self-adaptive surface. Forexample, there are the so-called foil bearings, whose structure isindeed different from that of the pocket sliders described in WO2004/053346. Said foil bearings have several characteristics in commonwith said pocket sliders (e.g. the capacity to function at highvelocities without liquid lubricants, etc.) but, at will be clearhereinbelow, they could never be used to carry out all the functionscarried out by the devices used in the present invention (for example,they could not carry out the function of sentinel element, etc.) withoutconsidering that the foil bearings are of much more difficult and costlyconstruction than the liquid pocket sliders or bumpers and that, unlikethe latter, they must be custom-designed for each specific application.

In U.S. Pat. No. 3,456,993, by G. Müller, a bearing constituted by amembrane containing a pressurized liquid supports a flexible foil, whoseface opposite that rested on the bearing is the active surface thatsupports a shaft in rotation. In such structure, the liquid pocketcarries out a function analogous to that of the so-called bump foil ofthe foil bearings, but the system described herein is not designed fortolerating the breakage of the foil, nor for exerting a stabilizing andself-centering action, or for predicting incipient failures. In thefollowing description, the particular bearings of the prior art that areemployed in an original manner by the invention, in a plurality ofdifferent and specific functions, will be called liquid pocket sliders(Liquid Pocket Sliders, abbreviated with LPS) since such name appearstechnically more correct than the name Liquid Pocket Bumper (LPB) usedin WO 2004/053346 for the same pocket sliders. The reasons will beunderlined for which by employing these LPS according to a particularshape and arrangement, it is possible to obtain the following positiveeffects:

-   -   tolerance and compensation of small misalignments between the        rotor and the stator;    -   elimination of the resonances;    -   diagnostic control of the device functioning, for the purpose of        preventing malfunctions;    -   elimination of the vibrations due to an imperfect balancing of        the rotor.

These problems are particularly important in the case of devices forcontrolling the attitude of a satellite. In such devices, the flywheelmust be able to rotate for years without direct human surveillance, sothat it is necessary to avoid the following as much as possible:

-   -   a) an excessive unbalance, indicated below with “e”,    -   b) a wear of the active surfaces (i.e. of the surfaces subjected        to relative sliding, under load) caused by the vibrations and/or        by the friction,    -   c) unexpected functioning irregularities.

Specifically, the essential part of the invention consist of placingthese special liquid pocket sliders—with a rest shape, a preload, and arigidity that are specially designed (and possibly with specialconstraints for the membrane of the liquid pocket)—around the outermostperiphery of the rotor, rather than placing conventional bearings (ballbearings, roller bearings, foil bearings, etc.) around the shaft of therotor, and conferring particular characteristics to one or more liquidpocket sliders that allow them to work as “sentinel elements”, whosepossible breakage does not involve any deterioration (or only anegligible deterioration) of the performances of the entire device (e.g.of a CMG, Control Moment Gyro satellite device).

In the following description, the theory underlying the presentinvention will also be described, together with a method for determiningthe preload and the characteristics of the liquid pocket LPS slidersmost suitable for eliminating the vibrations and the resonances from thedesign.

A structure of the device like that according to the present inventionwould not be possible by employing conventional bearings, for thereasons indicated above. Indeed, rolling bearings would not functioncorrectly at the extremely high linear velocities normally present onthe periphery of the rotors rotating at high angular velocity; aboveall, even only one damaged rotating/rolling element—such as a ball orroller—would inevitably cause damage to the remaining part of the CMGdevice.

Hereinbelow, the main base characteristics of the LPS bearings of theprior art are listed:

-   -   they are constituted by one or more sliders, rather than by        rolling elements such as balls or rollers;    -   such sliders are essentially formed by a flexible membrane with        high elastic modulus, which is fixed on a rigid structure and        closes, i.e. retains, a liquid;    -   they can operate without liquid lubricants (when the slider        slides on a relative slide surface it can create, due to viscous        drag, a gap traversed by air or gas with a specific velocity        profile, between the relative slide surface and the LPS slider,        and such air or gas acts as lubricant);    -   the lubrication occurs in a hydrodynamic manner due to the        air/gas in the environment where the device operates, only above        a critical velocity, which is a function of the properties of        the gas, of the load conditions, of the materials, etc.;    -   the active surface of these LPS sliders/bearings is the external        surface of the membrane that encloses the liquid. It is very        yieldable and hence, under the action of the lubricant,        spontaneously assumes the most efficient shape possible (i.e.        that which maximizes the load support capacity of the slider        itself), which in turn depends on the distribution of the        pressure generated inside said lubrication channel for any one        functioning condition;    -   at stationary functioning conditions and velocities, these        sliders work according to a perfect hydrodynamic condition, i.e.        in the absence of contacts with the active surfaces;    -   the rigidity of the LPS sliders can be actively adjusted both        when the device is at rest and when it works normally;    -   their capacity of adaptation of the surface to the distribution        of the pressures inside the lubrication channel is essentially        independent of their rigidity. This implies for example that the        rigidity of the LPS bearings can be modified without        considerable variations in the load support capacity by the        device at any given velocity;    -   an essential difference with respect to the ball bearings is        that their load support capacity increases with the increase of        the functioning velocity, also because the heat produced is        relatively little and hence the variations of the viscosity of        the lubricant are relatively small;    -   they are resistant to mechanical shocks to the extent in which        the tensile strength of the membrane and the compressibility of        the enclosed liquid are sufficient for absorbing such impact.

In the original structure proposed, any deflection of the axis of therotor from its nominal direction is directly opposed by the LPSsliders/bearings, which tend to be more loaded at the points towardswhich the rotor is moved, so as to exert a self-centering action on therotor. For small unbalancing of the rotor, the deflection of the rotoraxis—and hence the load overload of several elements of the LPSbearing—can never increase excessively since the reaction force thateach LPS is capable of rapidly exerting increases with the compressionof such LPS element. In addition, the LPS element that has sustained onesuch small overload continues to work in hydrodynamic condition and iscapable of reacting to the small deflections of the rotor withoutundergoing or causing an excessive increase of the friction and the heatgenerated on the affected surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of a merenon-limiting example by making reference to several particularembodiments thereof and to the relative theory/methodology, all shown inthe closed figures, in which:

FIG. 1 shows a movement vs. frequency (or pulsation) graph, for a mass Mfixed on a body with elastic constant k and subjected to an externalforce F(t) variable with frequency ω₁, the system assumed to have onlyone frequency thereof ω₀=(k/M)^(1/2) and only one degree of freedom, themovement being normalized with respect to the movement d₀ that therewould be if the force F was constantly applied with it maximumamplitude;

FIG. 2 shows a graph of the dependence of the ratio between themisalignment “d” and the unbalance “e” for a rotating system, on theratio between the rotation frequency (angular velocity) ω₁ of the rotorand the critical frequency (of resonance) ω₀ of the system; also in thiscase, the treatment is simplified by considering only one degree offreedom of the system;

FIG. 3 shows a diagram illustrating the quality comparison, in theabsence of preload on the rotor, between the effect due to thecentripetal force (exerted by the LPS sliders on the rotor) and to thecentrifugal force (it too acting on the rotor by virtue of the unbalance“e” and/or the movement=misalignment “d”), respectively; it is notedthat for d=d* the sum of the forces equals zero;

FIG. 4 very schematically illustrates the liquid pocket slider (8), orLPS slider, at rest and under load, respectively (with a squeezing δagainst a relative slide surface 2);

FIG. 5 shows various configurations, arrangements and constraints forthe LPS sliders; specifically:

FIG. 5 a) shows, in front perspective, nine (=3×3) LPS elements withhemisphere shape, with constraints (6) also called containment or cagewalls, considering, i.e. imagining, a specific square surface with areal² filled with said hemispheres; the constraints/walls (6) arrangedaround each hemisphere prevent any outward movement of the membrane (8or 9) of the slider which retains the liquid in the relative hemisphere;

FIG. 5 b) shows (always imagining the relative plan view on an area l²)four spherical caps LPS lacking constraints;

FIG. 5 c) shows (always imagining the relative plan view on an area l²)a single spherical cap LPS lacking constraints and having greater size;

FIG. 6 shows a qualitative graph of the load (W) vs. squeezing (δ); itis noted that the smaller the radius of curvature, the greater thereaction to the squeezing; the letters a), b) and c) refer to therespective cases of the preceding FIG. 5;

FIG. 7 shows the total force f_(T) on the rotor (given by the sum of thecentripetal reaction of the LPS bearing, shown above the abscissa, andthe centrifugal force, below the abscissa, due to the unbalance “e” andto the movement or misalignment “d” of the rotor with respect to theposition of the symmetry axis of the rotor in the rest state) for asystem of sliders, i.e. of LPS elements sufficiently preloaded forworking at a maximum angular velocity ω_(M) and in the presence of anunbalance “e” of the rotor itself; it is known that the greater thedesign velocity ω_(M), the greater the required preload will be; inaddition, so that f_(T) has a minimum in d=0, the greater the unbalance“e”, the greater the rigidity “dW/dδ” must be of the system LPS afterpreloading;

FIG. 8 is a schematic section view (orthogonal to the axis of the shaftof the rotor) of a particular structural shape of the device of thepresent invention, in a possible embodiment, with 4 LPS liquid pocketsliders of “sentinel cell” type (4), arranged in “strategic” positions(here at intervals of 90°) in order to obtain information regarding thedistribution of the load during the rotation of the rotor (5);

FIG. 9 is a view of an enlarged detail of FIG. 8, which in particularshows the constraints (or containment or cage walls) (6) that must beimagined to completely surround each element LPS (3; 4; 10), and asensor (7) associated with a LPS pocket or sentinel cell (4).

FIG. 10 is a view of a detail that represents the preloading cells (10)installed on the rotor (5) and provided with a generic device foradjusting the preload (11) and with a sensor (7) that can for example bea pressure sensor or a load cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTIONExplanation of the Self-Centering Functioning Principle of the Flywheel(or Rotor)

Generally, in mechanical or electromechanical systems, the causes of thevibrations are of various type. Consequently, each of these systems isusually characterized by multiple frequencies thereof.

Nevertheless, for the sake of simplicity, in the examples the case ofonly one degree of freedom will be examined. In any case, it is deemedthat this is sufficient for illustrating the underlying principle of theinvention.

d₀ is the movement of a mass M fixed to a body with elastic constant k,when a constant force F₀ is applied thereto. If a force is applied tothis system, but with an amplitude F(t) that varies with a frequency ω₁between 0 and F₀, then the movement d of the mass M will be given by theformula:

$\begin{matrix}{{d = \frac{d_{0}}{1 - \left( \frac{\omega_{1}}{\omega_{0}} \right)^{2}}}{{{where}\mspace{14mu} \omega_{0}} = {\sqrt{\frac{k}{M}}.}}} & (1)\end{matrix}$

When ω₀=ω₁ the system is in resonance (see graph of FIG. 1).

Now, a rotor is considered in which:

M=mass of the rotor

{right arrow over (e)}=distance of the center of mass of the rotor fromthe axis of the rotor (unbalance)

{right arrow over (d)}=ideal movement/misalignment of the axis of therotor from the rotation axis

{right arrow over (ω₁)}=angular velocity of the rotor

{right arrow over (ω₀)}=critical frequency of the system.

In this case, the rotor will be subjected to a centrifugal force which,in addition to rotating with an angular velocity ω₁, has an intensitydependent on the modulus of this angular velocity. Indeed: {right arrowover (F_(c))}=Mω₁ ² ({right arrow over (e)}+{right arrow over (d)}).

{right arrow over (ω₁)} and {right arrow over (ω₀)}, are generallydifferent from each other since {right arrow over (ω₀)} depends on thecharacteristics of the system while {right arrow over (ω₁)} is set by anexternal actuator. Nevertheless, the entire system will oscillate withthe same frequency as the centrifugal force, i.e. ω₁.

For a given unbalance e, F_(c) grows linearly with the movement d of theaxis of the rotor and as such constitutes a destabilizing force.

Any stabilizing force capable of opposing such centrifugal force in themachines of the prior art must be applied to the rotor by means of thebearings and the shaft, which therefore require being as rigid andbalanced as possible. The rotors supported by magnetic supports are anexception, which nevertheless imply an active control and much morecomplex embodiments. The present invention instead allows designingrather light rotor systems, with simple structure and without requiringactive control, at the same time relaxing certain requirements of thebearings.

If the system is not in resonance, an elastic force F_(e)=kd may becapable of balancing the centrifugal force.

Hence, in equilibrium conditions:

$F_{c} = {{M\; {\omega_{1}^{2}\left( {d + e} \right)}} = {{kd} = {{F_{e}.\frac{d}{e}} = \frac{M\; \omega_{1}^{2}}{k - {M\; \omega_{1}^{2}}}}}}$${{with}\mspace{14mu} \omega_{0}} = {{\sqrt{\frac{k}{M}}\mspace{14mu} {one}\mspace{14mu} {obtains}\mspace{14mu} \frac{d}{e}} = \frac{\frac{\omega_{1}^{2}}{\omega_{0}^{2}}}{1 - \frac{\omega_{1}^{2}}{\omega_{0}^{2}}}}$

Hence, for ω₁>>ω₀ the rotor will rotate around its center of mass, andfor ω₁=ω₀ the system will be in resonance. (see FIG. 2).

Hence, even in the presence of a small unbalance, a linear elasticreaction to the centrifugal force gives rise to vibrations andresonances. A shaft of the rotor which for small inflections obeysHooke's law, for example, constitutes an elastic system that has suchbehavior. Analogously, bearings of foil bearings type, even mounted onthe external periphery of the rotor, would not resolve the problem ofthe resonances (given that their reaction to the load is approximatelylinearly proportional to d, in the simplest structures).

In the present invention, the shaft does not have the task of generatingan elastic reaction to the centrifugal force acting on the rotor;rather, most of this function is completed by the liquid pocket sliders(LPS) mounted on the periphery of the rotor and which will be describedhereinbelow.

Now, the elastic reaction of such LPS sliders or bearings is not linear.For small deformations, it can be approximated by means of the formula:F_(LPS)≅k_(LPS)d².

Hence in equilibrium conditions we have:

M ω₁²(d + e) = k_(LPS)d² k_(LPS)d² − M ω₁²d − M ω₁²e = 0$\frac{d}{e} = \frac{{M\; \omega_{1}^{2}} \mp \sqrt{{M^{2}\; \omega_{1}^{4}} + {4k_{LPS}M\; \omega_{1}^{2}e}}}{2k_{LPS}e}$

Now, setting

${\omega_{*} = \sqrt{\frac{2k_{LPS}e}{M}}},$

one has:

$\begin{matrix}{{\frac{d}{e} = {{{\frac{1}{2}\frac{M\; \omega_{1}^{2}}{k_{LPS}e}} \mp \sqrt{\frac{{M\;}^{2}\omega_{1}^{4}}{4k_{LPS}^{2}e^{2}} + \frac{2M\; \omega_{1}^{2}}{2k_{LPS}e}}} = {\frac{\omega_{1}^{2}}{\omega_{*}^{2}} \mp \sqrt{\frac{\omega_{1}^{4}}{\omega_{*}^{4}} + \frac{2\omega_{1}^{2}}{\omega_{*}^{2}}}}}}{{Hence}\text{:}}\text{}{\frac{d}{e} = {\frac{\omega_{1}^{2}}{\omega_{*}^{2}}\left( {1 \mp \sqrt{\frac{\frac{\omega_{1}^{2}}{\omega_{*}^{2}} + 2}{\frac{\omega_{1}^{2}}{\omega_{*}^{2}}}}} \right)}}} & (2)\end{matrix}$

Therefore, when ω₁>>ω_(*), the following solutions are obtained:

$\begin{matrix}{\frac{d}{e} = {- 1}} & \left. a \right) \\{and} & \; \\{\frac{d}{e} = {2\frac{\omega_{1}^{2}}{\omega_{*}^{2}}}} & \left. b \right)\end{matrix}$

in which the formula a) is obtained by applying l'Hôpital's rule.

Solution b) does not have a physical significance since the system isexternally constrained. Consequently, d=−e i.e. the rotor tends torotate once more around its center of mass, such that, with e≠0, itvibrates.

The only difference with respect to the preceding case (centrifugalforce balanced by an elastic linear force of F_(e)=kd type) is thatresonances are no longer in the picture.

This is already a good result, but the objective is that of eliminatingthe vibrations as well. The solution consists of a suitable preloadingof the LPS sliders or bearings.

It must be observed that such preloading must always be in phase withthe centrifugal force, which rotates with frequency ω₁. Hence, in theembodiments of the present invention in which it is desired to eliminateeven the vibrations of limited amplitude, in addition to the resonances,the simplest thing to do will be to obtain several special cells, withthe function of preloading cells (10), directly on the rotor, with therelative slide surface obtained on the internal surface of the stator.Of course, if the other LPS elements (3; 4) are fixed to the internalsurface of the stator (2), the preloading cells (10) must be fixed onthe rotor (5) in a different axial or radial position in order to notinterfere with the other LPS elements (3; 4) during rotation. Each ofsuch preloading cells will be provided with a pressure sensor like thesentinel cells 4, as well as with preloading means, as in claim 7,adapted to adjust the internal pressure thereof in a manner independentfrom all the other cells. In this manner, the preloading cells, fixed ina sufficient number on the external surface of the rotor, will rotateintegrally therewith, necessarily in phase with the centrifugal force tobe balanced.

Operatively, the preload necessary for eliminating the vibrations at agiven design speed ω_(M) can be obtained by employing the followingprocedure:

-   -   1. all the preloading cells are pressurized at a same initial        pressure;    -   2. the rotor is made to rotate at the velocity ω_(M) and the        pressure variation produced inside each preloading cell is        measured, such variation due to the non-uniform distribution of        load due to unbalance;    -   3. the rotation is stopped, and through the aforesaid preloading        means, a pressure distribution similar to that detected when the        rotor rotated at the velocity ω_(M) is obtained inside the        preloading cells.

At this point, the rotor will be balanced at the velocity (D_(M).

Let's examine, mathematically, how a suitable preload is capable ofeliminating all the vibrations.

Set k_(LPS)d²=Mω_(M) ²e, and seek the value d* that compensates for thecentrifugal force (=Mω_(M) ² e) for a null movement.

This corresponds with the desired preloading.

One obtains d*=±√(Mω_(M) ²e/k)=±ω_(M)√(Me/k) with ω_(M)=maximum designvelocity, and k≡k_(LPS) for simplifying the formulas.

The preloading condition for the LPS bearings becomes:

Mω ₁ ²(d+e)=k(d+ω _(M)√(Me/k))²  (3)

By solving the quadratic equation (3) in d, one obtains a discriminant

Δ² =M ²ω₁ ⁴−4 √kω _(M)√(Me)Mω ₁ ²+4kMeω ₁ ², from which

for ω₁→ω_(M) Δ²=(M·ω_(M) ²−2√kω_(M)√(Me))² and a solution, always forω₁→ω_(M)

d=(2kω _(M)√(Me/k)−Mω _(M) ²±Δ)/2k i.e. d ₊=0.

From this it follows that for ω₁→ω_(M), d→0.

Instead,

$d_{-} = {{2\omega_{M}\left. \sqrt{}\left( {{Me}/k} \right) \right.} - \underset{k}{{\underset{\_}{M\; \omega}}_{M}^{2}}}$

The latter solution is to be discarded since the rotor system isconstrained and d therefore cannot assume large values.In addition, however, the rotor must also be stable.Hence, for d=0 it must hold true that the total force

F(d)=k (d+ω_(M)√(Me/k))²−Mω₁ ²(d+e) meets the minimum condition, i.e.:

F′(d=0)=2 ω_(M) k√(Me/k)−Mω ₁ ²=0

i.e.:from which, by writing

4ω² _(M) kMe=M ₂ω⁴

$\frac{\omega_{M}^{2}e}{d^{*2}}$

in place of k:

$\frac{4\omega_{M}^{4}M^{2}e^{2}}{d^{*2}} = {M^{2}\omega_{1}^{4}}$

-   -   and therefore:

$\begin{matrix}{d^{*} = {2{e\left( \frac{\omega_{M}}{\omega_{1}} \right)}^{2}}} & (4)\end{matrix}$

Therefore, in order to prevent all vibrations, the preload d* must begreater the greater the unbalance and the further away the workfrequency from the maximum design frequency. We recall that thecondition (4) is valid in our simplified approximation that theresultant of the forces that are opposed to the centrifugal force is ofthe type F_(LPS)≅k_(LPS)d². Nevertheless, it is clear that the ideaunderlying the invention remains valid even if the precise form of saidresultant of the forces that is opposed to the centrifugal force isslightly different.

The same concepts can be graphically illustrated since this constitutesa qualitative though perhaps more direct method.

In addition, the following considerations can be useful forunderstanding the role carried out by the shape of the LPS sliders andthe reason for which the correct selection of this shape is soimportant.

With reference to FIG. 3 enclosed with the present patent application,for the sake of simplicity it is assumed that ω₁=ω*=ω (less favorablecondition) and that, at rest, the rotor is perfectly aligned withrespect to the central line thereof, i.e. that d(ω=0)=0. It is assumedthat the LPS bearings barely touch the rotor, without any preloadingagainst the latter. Then, when the system begins to rotate, d tends toincrease until it reaches the value given by the preceding equation (2)(1+√3)e, and the centrifugal force will do the same. With the increaseof d, the centripetal reaction of the LPS bearings also increases, butwith a different law (˜d²), and finally it balances or compensates forthe centrifugal force.

The distance d* (FIG. 3), for which the centripetal reaction of the LPSsliders or bearings balances or compensates for the centrifugal force onthe rotor, can be canceled out by suitably preloading these LPS sliders,as was shown above. In such a manner, for a given velocity of the rotor,the minimum energy U of the system is reached when the axis of the rotorcoincides with the central line of the system, also in the presence of asmall unbalance or misalignment of the same rotor (see FIG. 7, totalforce f_(T)).

The system is stable at the minimum of the curve:

U(x)=−∫_(x) ₀ ^(x) F(ξ)dξ+U(x ₀)

where F(ξ) is the total force as a function of the movement.

Since such reasoning is valid, the tilt or slope of the centripetalreaction curve of the LPS liquid pocket thrust bearing must be greaterthan the slope of the centrifugal force due to theunbalance/misalignment, at the point where the two absolute valuescompensate each other.

Such condition is verified so long as one correctly selects the shape ofthe LPS bearings. With the term “suitable preloading” of the LPSsliders, it is intended that one must take under consideration all ofthese factors.

Now, while for e≠0, the absolute value of the centrifugal force for d=0varies like ω², the absolute value of the centripetal reaction of theLPS sliders is only determined by the preloading and does not vary withthe rotation velocity. Hence, it always remains extremely important tohave well-balanced rotors available.

That said, even a relatively large misalignment of the axis of the rotor(due to a relatively flexible shaft in the presence of transversegravity, for example) can be tolerated since it can be more easilycompensated at low velocities (i.e. immediately after starting, beforethe machine reaches greater velocities). Certainly this constitutes animportant advantage with respect to the conventional machines, since therequirement relative to the rigidity of the shaft can be less severe.

A suitable preload can only be established by taking under considerationthe shape of the LPS liquid pocket sliders or bearings and theirinternal pressure.

The pressure jump across the membrane is given by the generalizedLaplace formula,

${\Delta \; P} = {\tau \left( {\frac{1}{R_{1}} + \frac{1}{R_{2}}} \right)}$

where R₁ and R₂ are radii of curvature of the surface of the membraneand the tension of the membrane depends on the surface area of themembrane (this does not hold true for liquids, where the surface tensiondoes not depend on the surface area of the liquid).

The load that the air film (or air channel formed between the LPSbearing and the relative slide surface) must sustain is approximatelygiven by the product between the area of the flattened part of themembrane (contact area) and the pressure drop across the membrane. Thepreload is determined by the tension τ of the membrane, by the initialshape of the non-deformed membrane (without the load) and by thesqueezing δ of the LPS slider against the relative slide surface (forexample the surface of the flywheel); see FIG. 4.

The tension also depends on the elastic modulus E, which constitutes aproperty of the material. Hence, for any one given material, and adefined initial shape, the graph of the load (W) can be designed as afunction of the squeezing (δ).

Hereinbelow in the present description, reference will be made to FIG. 5and to the corresponding FIG. 6.

The following example shows that a particular geometric configurationaffects the rigidity of the LPS system, for a given area l².

The present invention, indeed, regards a self-centering rotor in whichthe geometric configuration of the LPS systems mounted on the periphery(edge) of said rotor is selected in a manner so as to optimize therigidity of the LPS slider or bearing, in order to obtain a stablesystem at the maximum possible value of ω and for a maximum of theestimated value of the unbalance “e” (such unbalance “e” must in anycase be reduced to the minimum possible during the manufacturing of therotor).

In other words, such geometric configuration tends to be that whichmaximizes the variation of the curvature of the surface of the membrane8 of the LPS bearing, for a specific squeezing (δ), with respect to thesystem not subjected to the load. The present invention also includesthose cases in which the condition of optimization (maximization) of thecurvature of the surface for a given squeezing (δ) with respect to thenon-loaded system, is also obtained by taking under considerationpossible design requirements/parameters, which could lead to a shape ofthe LPS membrane different from the ideal theoretical form.

With reference to FIG. 5, a specific square surface with area l² can befilled with different LPS configurations, as the abovementioned figureshows. The LPS pocket sliders of case a) are constrained by a wall (6)that prevents any movement of the membrane (8) (of the LPS slider)towards the outside, so as to oblige the membrane (8) itself to bend,with a lower radius of curvature than an analogous non-constrainedmembrane (8). See for example the diagrams of FIG. 6 with regard to thebehavior under load of such systems of LPS sliders. In FIG. 6, it isalso noted that the smaller the radius of curvature, the greater thereaction to the load W. The letters a), b) and c) refer to the cases ofFIG. 5.

Now, returning to FIG. 5, as stated above, the containment walls 6 ofcase a) oblige the membrane (8) to be bent more than a membrane that isnot constrained. In order to correctly carry out its function, saidcontainment walls must be tangent to the surface of the membrane (8)along its fixing line, i.e. along the peripheral line where the membrane(8) “comes out” from the rigid structure to which it is fixed. Normally,such rigid structure is movable so to be able to move the slider fromthe rest condition (FIG. 4, left side) towards the preloading conditionagainst the relative slide surface (FIG. 4, right side), or thepreloading could be obtained by increasing the internal pressure of theliquid (“swelling” or injecting liquid) inside the pocket of the slider.

Finally, FIG. 7 shows the total force f_(T) acting on the rotor, givenby a system of liquid pocket sliders (LPS) or bearings having a preloadsufficient for being able to work at a maximum design angular velocityω_(M) and in the presence of an unbalance “e”; it is observed that thetotal force f_(T) (vectorial sum of the centrifugal force and thecentripetal reaction) must have a minimum for d=0 in order to ensure thestability of the rotor 5.

In FIGS. 8 and 9, an embodiment is shown in which the liquid pocketsliders (LPS sliders) (3) are mounted on the stator (2), while theexternal (cylindrical) surface of the rotor (5) constitutes the relativeslide surface, i.e. the surface which faces directly on the internal(cylindrical) surface for mounting the LPS bearings on the stator (2).First of all, it is observed that also the numbers (4) and (10) indicateliquid pocket sliders (LPS sliders or bearings), but that these (even ifthey substantially have many characteristics in common with the LPSsliders indicated with the reference number (3) in this specificembodiment of the invention) constitute the so-called “sentinel cells”(4) or the so-called preloading cells (10), whose function will beclarified hereinbelow in a thorough manner.

In addition, it is observed that the configuration for mounting the LPSsliders (3) and (4) could be reversed with respect to the embodiment ofthe invention shown in FIGS. 8 and 9; i.e. said sliders (3) and (4)could be arranged on the external surface of the rotor (5), which wouldthen constitute the mounting surface that faces the internal surface ofthe stator (2), the latter then representing the relative slide surface.

Before describing the functioning and significance to be associated withthe sentinel cells (4), it is observed that in order to have a specificinitial preloading of the LPS sliders against the relative slidesurface, it is suitable to provide for mechanical means that allowadjusting such preload. The preloading means of the liquid pocketsliders (3; 4) advantageously comprise a movable structure (for the sakeof simplicity not shown in FIG. 8 and FIG. 9), on which the LPS slideris directly mounted, as well as mechanical actuators (e.g. a smallpiston, also not represented in FIGS. 8 and 9) in order to press therelative LPS slider (3; 4; 10), causing the squeezing (6) thereofagainst the relative slide surface (or according to the modes statedabove, and as specified in claim 7).

The sentinel cells (4) and their essential advantages will now bedescribed in more detail.

Tolerance for Possible Failure and Opportune Detection of an IncipientDeterioration.

A certain number of liquid pocket sliders, pressurized independentlyfrom each other, arranged around a rotor in the above-described manner,are capable of obtaining a failure-tolerant system of LPS sliders.Damage caused to the single balls of a conventional ball bearing, due toa failure of the check means or to the wear or degradation of thelubricant, could cause a rapid deterioration of the performances and inthe end even a series of functioning irregularities of the entiremechanism. Damage or even breakage of a single,independently-pressurized liquid pocket of a LPS bearing, would howeverlead to the immediate depressurization of the membrane (8) or (9) thatis broken, which therefore would no longer sustain the load, but wouldno longer produce damage to the rotor (5).

In this manner, if a sufficient number of pressurized pockets remainpressurized, the system would not undergo any damage and the mechanismcan continue to function.

If a sufficient number of LPS sliders all work together simultaneously,the breakage of only one of these involves only a negligible increase ofthe load for the remaining sliders, so that the performances of thesystem remain substantially the same. The tolerability of the breakageof a single liquid pocket element was already shown in WO 2004/053346.In the present invention, the concept is used by introducing LPS sliderswith the single, specific function of preventing failures; such functionwas not contemplated in the previously cited invention.

Indeed, several LPS sliders can be specially obtained in a manner so asto be weaker than the other LPS sliders, which we will call “ordinaryLPS sliders”; the weaker LPS sliders will be called “sentinel cells”.

Such sentinel cells can be obtained in a manner so as to have limitedsize, in order to support a total load percentage that is as low aspossible, reinforcing the concept according to which the failure of asingle sentinel cell does not affect the overall performance.

Under certain aspects, a sentinel cell functions as a fuse of anelectrical apparatus, in the sense that the breakage of the sentinelcell indicates that an operating limit has been exceeded, given that thesentinel cell is specially made to be the weakest component of thesystem.

An important difference with respect to the electrical fusesnevertheless consists of the fact that if a LPS sentinel cell “burns”,this does not stop the system, since the system can be failure-tolerantin the sense clarified above. On the contrary, the breakage of asentinel cell simply signals the need to substitute/renew the system ofbearings.

Another difference with respect to the electrical fuses is that the LPSsentinel cells do not serve to protect the remaining part of the systemfrom damage: they represent diagnostic means rather than protectionmeans.

The sentinel cells 4 work in parallel with the other ordinary sliders(3), while an electrical fuse works in series. The LPS sentinel cells(4) can also sustain a breakage due to a process of progressivedegradation due to the prolonged functioning, rather than following anunsupportable/unsustainable variation of their operative conditions.

In the case of automatic functioning without direct human supervision,such as for the bearings of a CMG device for controlling the attitude ofa satellite, the failure of a sentinel cell could thus make a possiblesystem failure predictable, thus placing the control from Earth in theconditions for adopting appropriate countermeasures.

An opportune signaling of the incipient deterioration of a LPS bearingprovided with sentinel cells is easily obtainable by monitoring the LPSsentinel cells, so as to readily detect their possible irregularities.Such monitoring can be implemented by means of sensors (7), as indicatedin FIG. 9. For example:

-   -   a pressure sensor, capable of detecting the variation of the        pressure inside the LPS membrane, would immediately signal the        breakage of the membrane and its consequent depressurization;    -   a load cell could be used for detecting the variation of the        load due to the breakage of the membrane;    -   optical means could detect the significant variations of the        shape of the membranes of the sentinel cells, which could be the        consequence of a breakage thereof;    -   a temperature sensor, which measures the temperature of the        liquid inside the LPS sentinel cell, could indicate an irregular        variation of the temperature as a consequence of the loss of the        liquid.

It is underlined that the above-listed means for detecting the breakageof a sentinel cell or of its irregular functioning are to be consideredas merely exemplifying. Thus, it is easily comprehensible that the useof other detection means in the sentinel cells could not be claimed asan invention in itself.

In principle, the radial load on the LPS elements does not have to bedistributed in a uniform manner all around the flywheel. Therefore,several LPS elements could be more stressed than others. In order toaccount for such possibility, the sentinel cells will be positioned inkey, i.e. strategic positions, in order to monitor the operatingconditions at several points of the system.

Indeed, by providing such sentinel cells with specific sensors, thesystem would have the further characteristic of being capable ofdetecting irregularities or non-nominal functioning conditions. Forexample, a pressure sensor in each sentinel cell could monitor therelative internal pressure, which in turn is correlated with the localconditions of the load. This would constitute an element/important pieceof information, since a non-uniform load distribution around theflywheel could cause a premature breakage of several liquid pocketsliders (LPS sliders) of ordinary type (i.e. in addition to the breakageof a sentinel cell). Thus, the function of the sentinel cells would notbe limited to supplying information only of “yes/no” type: they couldalso supply a more complete view of the general functioning conditionsof the device, making possible the integration of their information withother data/information elements coming from other sources.

Therefore, the present invention has various aspects and advantages thatdistinguish it from the prior art. While a flywheel of the prior art wassupported by ball bearings or roller bearings of conventional typearound the rotation shaft thereof, according to the present inventionthe same flywheel is automatically supported and centered by a pluralityof independent LPS bearings, in the sense that the breakage of one ofthese causes at most the outflow of a small quantity of liquid which isdispersed in the surrounding environment without interfering with thefunctioning of the other LPS liquid pockets. The heat generated in thesliders/bearings, in addition to being lower, is transferred and quicklydispersed through the liquid contained in the pockets. Once again, thebreakage of a sentinel cell (which also carries out the function ofbearing) signals the possibility of a failure to the system in aspecific subsequent period, and hence the sentinel cells act asdiagnostic means (in order to then take possible countermeasures) whichdo not interfere with the functionality of the system. The monitoring ofsuitable sensors associated with the sentinel cells, also in the absenceof the breakage thereof, can supply useful information on the overallfunctioning, indicating for example irregular distributions of loadbetween the various LPS elements. Finally, several cells provided withindependent sensors and preloading means can be obtained on the rotor,rather than on the stator, so as to be able to introduce a preloadalways in phase with the centrifugal force connected with possibleunbalancing of the rotor itself, in a manner so as to completely cancelthe vibrations at a certain design velocity. Therefore, the presentinvention, applied in particular to a flywheel of a CMG device of asatellite, supplies many advantages not easily intuitable by the manskilled in the art.

1. Rotation device comprising: a rotor (5) integral with a rotationshaft (1), a stator (2) coaxial with the rotor (5) and which facesdirectly on the external periphery of the rotor (5), forming an annularinterspace with respect to the latter, liquid pocket sliders (3; 4; 10)comprising a membrane (8) for containing a liquid and functioning asradial bearings during the rotation of the rotor (5), said membrane (8)being characterized by a tension (τ) and by a high elastic modulus (E),i.e. substantially rigid upon traction, said rotation device providingfor means for preloading the liquid pocket sliders (3; 4; 10) against arespective relative slide surface, characterized in that said liquidpocket sliders (3; 4; 10) are mounted inside said peripheral annularinterspace by fixing the edge of their membrane (8 or 9) to a mountingsurface inside the stator (2) or to a mounting surface outside the rotor(5), the surface opposite the mounting surface constituting saidrelative slide surface; and wherein, given an estimated maximum of thepossible unbalance (e) of the rotor (5), and given a maximum designangular velocity (ω_(M)) of the rotor (5), the centripetal reactionforce exerted by said liquid pocket sliders (3; 4; 10) on the rotor (5)is such to prevent resonances by limiting the amplitude of theoscillations due to possible small misalignments between the rotor (5)and the stator (2) and/or due to the centrifugal force Mω²e for eachrotation velocity ω≦ω_(M), given that “M” is the mass of the rotor (5)including the shaft (1); and wherein the elastic rigidity (dW/dδ) ofsaid liquid pocket sliders (3; 4) is such that the total force (f_(T))acting on the rotor has a local minimum at d=0.
 2. Device according toclaim 1, characterized in that at least one of said liquid pocketsliders (3; 4) constitutes a sentinel cell (4) adapted to detect anexcessive load or an excessive wear which has possibly caused thebreakage of its membrane (9) over time.
 3. Device according to claim 2,characterized in that said at least one sentinel cell (4) is associatedwith a pressure sensor (7) for continuously or intermittently measuringthe internal pressure of the liquid retained by the membrane (9), so asto verify possible liquid losses outside the relative liquid pocketslider (4).
 4. Device according to claim 2, characterized in that atleast one of said sentinel cells (4) has smaller size than that of theother liquid pocket sliders (3) of ordinary type, which do not have thefunction of predicting possible device failures, and therefore suchsentinel cell (4) supports a smaller percentage of the total load withrespect to a liquid pocket slider (3) of ordinary type.
 5. Deviceaccording to claim 2, characterized in that said sentinel cells (4) arearranged in strategic positions for constantly or intermittentlymonitoring the possible non-uniform distribution of the load on therotor, i.e. around the rotor itself, given that they are preferablyarranged at regular intervals from each other and between the liquidpocket sliders (3) of ordinary type.
 6. Device according to claim 2,characterized in that each of said sentinel cells (4) is associated withone or more sensors (7) of different type, adapted to detect thebreakage thereof and/or the variation of the sustained load, saidsensors (7) being selected for example from among the following types:pressure sensors; load cells; optical sensors; temperature sensors. 7.Device according to claim 1, characterized in that said means (11) forpreloading the liquid pocket sliders (3; 4; 10) comprise a movablestructure and actuators for causing the relative compression between theslider (3; 4; 10) and said relative slide surface, or said preloadingmeans (11) comprise means for varying the internal pressure of theliquid in the liquid pocket slider (3; 4; 10).
 8. Device according toclaim 1, characterized in that the rigidity (dW/dδ) of said liquidpocket sliders (3; 4; 10) is adjusted by employing one or more of thefollowing measures: adjusting the internal pressure of the liquid, byacting for example with a small piston that pushes the liquid from atank communicating with the liquid pocket interior through a respectiveduct; providing for a surface with curvature that is even non-uniform,but is adapted in the non-stressed rest condition for the surface of themembrane (8) of the liquid pocket slider (3; 4; 10); providing for asuitable squeezing (δ) once the following are set: the materials of theliquid and the membrane (8) containing it, the internal pressure of theliquid, as well as the shape of the membrane (8) of the slider (3; 4;10) for δ=0; providing for cage/containment walls/constraints (6) alongthe edges of the membrane (8) at its edge for fixing to the mountingsurface.
 9. Device according to claim 8, wherein said cage/containmentwalls/constraints (6) constitute stops that limit the maximumoscillation amplitude of the rotor (5) and which are formed by materialswhich minimize the damage to said relative slide surface in case ofcontact.
 10. Device according to claim 2, characterized in that asufficient number of LPS elements (10) are fixed on the rotor (5) so asto be able to introduce a preload in phase with the centrifugal forcedue to the unbalance “e” of the rotor (5), capable of balancing saidcentrifugal force at a specific velocity.
 11. Device according to claim2, characterized in that the membrane (9) of the sentinel cells (4) isadapted to be broken before the membrane (8) of the other types ofliquid pocket sliders (3; 10) by virtue of the fact that it has one ormore of the following characteristics: its thickness is calibrated in amanner so as to be smaller, e.g. 50% smaller, than that of the membrane(8) of the other types of liquid pocket sliders (3; 10); its material isdifferent and less resistant than that of the membrane (8) of the othertypes of liquid pocket sliders (3; 10); it has an anti-wear and/oranti-friction surface coating with calibrated thickness smaller thanthat of the other types of liquid pocket sliders (3; 10); it has ananti-wear and/or anti-friction surface coating of less resistantmaterial than that of the other types of liquid pocket sliders (3; 10).12. Device according to claim 1, characterized in that axial thrustbearings are also provided, or simultaneously both radial and axialthrust bearings are provided (radial/axial with regard to the thrustdirection), wherein at least one of these, but preferably all,constitute liquid pocket sliders.
 13. Device according to claim 1,characterized in that the cage/containment walls/constraints (6)provided along the edge of the membranes (8; 9) are tangent to thesurface of the membranes (8; 9) at their fixing edges or lines. 14.Device according to claim 1, characterized in that it constitutes aso-called CMG (Control Moment Gyro) device for controlling the attitudeof a satellite, wherein the rotor (5) comprises a flywheel (5) which isdriven by a motor.
 15. Device according to claim 14, characterized inthat said liquid pocket sliders having the function of radial and/oraxial thrust bearings during the rotation of the flywheel (5) aremounted on the external radial surface of the flywheel (5), which thusconstitutes said mounting surface.
 16. Device according to claim 1,characterized in that if the device constitutes a part of a turbomachine, a pump, a turbine, a compressor or the like, then the rotor (5)comprises, in addition to a system of blades or the like, also a ringwhose external surface forms a mounting or slide surface for the liquidpocket sliders (3; 4; 10).
 17. Device according to claim 1,characterized in that at least several liquid pocket sliders (3; 4; 10),but preferably all, are pressurized independently from each other, inorder to make the device failure-tolerant.
 18. Method for optimizing thefunctioning of a flywheel of a control moment gyros device and foropportunely preventing the failures thereof which comprises using thedevice according to claim 1.